In The Stairwell
by GlitterGod
Summary: Simon Lewis can't get enough of Isabelle Lightwood, but will one momentary loss of judgment cause more chaos than it's worth? Sizzy o/s. Mature readers.


**A/N: A quick Sizzy O/S. No copyright infringement intended. Mature content.**

* * *

_No one will find out._

Simon Lewis froze at the mention of his name, his eyes wide with horror. Somewhere in the apartment, Alec was calling out for him.

"Don't stop," Isabelle breathed out, her body resting limply against the stairwell wall.

They hadn't gotten two feet inside of Magnus's loft before the hunger he'd been so desperately trying to suppress took hold. In his mind, Simon could think of only two scenarios, both of them ending with his demise—either Alec would stake him on the spot for drinking from his sister, or Magnus would behead him for openly biting someone when the downstairs neighbor could walk out of their apartment at any minute.

"Simon…" Isabelle moaned softly, snapping Simon from his morbid thoughts.

Her pale hand reached up and fisted into his hair, forcing Simon to bite down harder against her neck. She flinched, only momentarily, before her body relaxed again as it always did. The bite from a vampire was erotic to begin with, but their secret rendezvous in the stairwell was turning Simon on to no end. Part of him actually enjoyed sneaking around like this. The other part was smacking him in the face, begging for some kind of rational thought to take over. He couldn't count on Isabelle being the voice of reason. She was well past caring at this point.

"Iz," said Simon as he reluctantly withdrew his fangs. Another shout echoed through the apartment, and spilled into the open stairway. Alec was on a mission. "Your brother is coming."

"I—I don't care," she answered numbly. "He's a big boy. He can handle it."

"That might be true, but I'm not sure I can." Simon licked over his lips, his fangs sliding back into place. The taste of Isabelle's blood was electric, and it was taking everything Simon had to hold it together.

"Don't bwe swuch a bwaby," she slurred. Another side effect of being bitten, it made people delirious.

Isabelle's dark eyes were glazed over, blood shot and clearly high off euphoria. How the hell was he going to face Alec when his sister was completely fang-drunk? Frankly, that was the least of his worries. As Simon steadied Isabelle against the wall, he felt the strain in his pants grow to unbearable means. _Fuck!_

"Has _anyone_ in this house seen Simon?!" Alec yelled again, his voice traveling down to where Simon and Isabelle were hiding.

_Maybe I can close the door. Maybe Alec won't notice_. Sure, they were great thoughts, and with the speed of a vampire it might be possible, but Isabelle had started to giggle and hiccup, and there was no telling what kind of fuss she would put up if he left her alone—even for a small moment.

"Shh, Izzy!" he whispered, placing a finger against her smudged, red lips.

Isabelle bit his finger. "Rawr! I'm a vampire!" she laughed, a little too loudly for Simon's liking.

Simon winced, although her bite was soft and far from painful. He was more concerned with the pair of voices near the top of the stairs. Magnus had come to see what all the commotion was about.

"Why are you shouting?" Magnus asked Alec.

There was a rustle, like plastic bags being tossed about after a shopping trip, and then the slamming of a cabinet. "I did what you asked," Alec stated. "I went down to the butchers, and bought a whole six pack of _pig blood_." Simon could actually feel Alec shudder. "And I come home today to find it all gone—_just gone!_"

_Aw, crap_, Simon thought. _The blood_. He'd meant to replace it today, to not draw suspicions to the fact that Simon didn't really need the blood, and they had accidentally spoiled it anyway. He and Isabelle had gotten a little freaky last night when Magnus and Alec were on a date, and most of the blood had fallen over on the shelf when Isabelle had shoved him against the fridge. It had taken less than an hour to mop up the mess after they were finished, but replacing the blood had completely slipped Simon's mind once Isabelle's hands had made their way down his pants on their way home tonight.

"I'm sure there's a logical explanation," Magnus was saying as Simon shook his head to clear away the memory of last night.

"Just like there's a logical explanation as to why his boxers were in the living room this morning?" Alec snorted.

"Boxers schmoxers," Isabelle snickered drunkenly.

_Oh, you've got to be kidding me! Izzy, you said you picked everything up!_ Simon groaned internally, and covered Isabelle's mouth. She proceeded to lick at his palm like Chairman Meow lapped at his evening milk.

"Oh, Lilith!" Magnus made a sound Simon couldn't identify. "Not on my new furniture. _Please _tell me they were not on the couch. I sat there this morning."

There was a small laugh, and then the sound of a short kiss. "Come on, take a walk with me. I need to get some things from the Institute and maybe it'll help me calm down if you go with me."

_Crap, crap, double crap!_ Simon had two choices. One, run like hell. Two, carry Isabelle upstairs. Either way, the proverbial shit was about to hit the fan. Opting for the easiest route away from the love birds creeping closer, Simon lifted Isabelle into his arms and prepared to make a run for it.

"Stop. Right. There. Daylighter." It was Alec. "What in the name of the angel have you done to my sister?"

Simon tensed, his jeans rubbing against his stiff cock as he kept his back to Alec. This was going to be bad. "She just had a little too much to drink at Taki's. I was going to get her some fresh air," he lied.

The sound of boots on the stairs seemed never ending, loud and ominous. "Isabelle drunk?" Magnus asked, amused. "Now this is something I need to see for myself."

"Me too," said Alec, without a single trace of humor.

Simon dared not turn around. "Honestly, guys, I've got her," he said, inching down the stairs.

"I got bitten!" Isabelle blurted out. "Bitten and smitten!"

"Smitten?" Magnus chuckled. "You're starting to sound like me."

"Bitten?" Alec chimed in. "Was it a demon? Where have you two been? What's going on here?"

It was like being put on display for the entire Clave to see. Alec and his Law. Always the Law. "Stop with the third degree. She's fine." He was almost to the front door.

"Fine as wiiiine," Isabelle sang out.

"Put my sister down so I can take a look at her," Alec demanded. "There's something fishy going on here. She could be infected."

"_Infected?!_" Simon hadn't meant to sound so offended, but since he'd been the one doing the biting, it was like Alec saying there was something wrong with him. "Trust me—she's not infected by any demons, just drunk. I'll bring her back safe and sound."

"I said put her down." Alec's voice was sharp and full of authority.

What choice did he have? Simon set Isabelle on her feet, and with a long, drawn out sigh he turned around, keeping Isabelle in front of him like a shield. Not because he was afraid of being hit, but because he didn't need a scene about what was happening in his pants. "See, she's fine," he said, peeking over Isabelle's shoulder.

"See, I'm fine," Isabelle mimicked, swaying slightly. "But _you_," her finger pointed toward Magnus, "are looking very canoodley tonight, Mr. High Warlocky! F-I-N-E spells FINE!"

"Canoodley?" Alec's blue eyes nearly bugged right out of his skull, and if Simon wasn't mistaken his heart gave a rapid thump.

"She's out of her mind," Magnus groaned, rolling up his sleeves as though he were about to perform some dramatic spell on Isabelle to bring back her senses. But his cat eyes soon widened as he realized what was really going on, and his hand reached out to stop Alec. "Why don't you let them handle it, darling?"

Simon flashed a pleading look toward Magnus, but it was too late.

Alec was immediately assessing Isabelle for injuries, ignoring all the commentary and in full Shadowhunter mode. It wasn't hard to tell where the issue was. Two streaks of crimson ran the length of Isabelle's neck from the tiny puncture marks Simon's fangs had left behind. "You bit her!" Alec shrieked. "You bit my sister!"

Isabelle's lips curled into a lopsided smile. "That's not alllll he did!" she sang again.

"Izzy!" Simon bellowed.

Alec stepped back, his cheeks flushing scarlet. "Step away from Isabelle before I do something drastic."

"I—I can't," Simon grumbled. You would think an impending fight would stop the need arising in his jeans, but _oh no_. Isabelle's blood was fueling his erection like gasoline poured on a fire.

Alec pulled a seraph blade from his back pocket. "Step away."

"Now, now, Alexander," Magnus interjected, a worried look crossing his face. "You know Simon drinks from Isabelle sometimes. This is no secret. Let them be, and we will go for that walk."

Alec shrugged off Magnus. "I'm not pissed about the biting," he stated. "I'm pissed that I had to walk all the way uptown to get _pig blood_ when the vampire is taking his meals from my _SISTER_!"

"About that…" Simon raised his hands after propping Isabelle against the doorway. He had no choice but to hope no one noticed the bulge. Unfortunately, like many things in the world, Magnus noticed right away and his strange eyes quickly focused elsewhere. Alec was too enraged to spot the problem, so Simon carried on. "You going to get blood for me was really nice. So, thanks for that. It's just…pig blood is a little—"

"Grosssss!" Isabelle giggled.

Alec's face darkened. "You said you wanted pig's blood."

"It was a liiiieee! We wanted sexy time," Isabelle said, stumbling forward. "Which you inter—interrupted." She hiccupped and jabbed Alec's shoulder. "Bad brother."

"I can see that." Alec looked unphased as he finally glanced at Simon's crotch, but his hand tightened on the hilt of his blade. "You've got all of ten seconds to run, Simon. If I catch you, you're a dead man."

"He's already dead," Isabelle blatantly pointed out. "Bossy boots! My boyfriend, not yours!"

Suddenly, Alec flung himself at Simon. They collided and crashed through the front door, out into the alley where Alec pinned him against the far wall. Simon was choking, gasping for air he didn't need. The force of their impact made him sputter and cough, and just when Simon thought he could take no more, just when he was about to fight back, Alec's hand smashed into Simon's groin.

Simon's eyes flew open in shock, only to find himself in even stranger surroundings than before. Something was different, something was off. Instead of the icy blue eyes he'd been facing moments ago, the deep and dark eyes of Isabelle Lightwood gazed back at him. "Hey, what are you afraid of?" she asked quietly, her hand sliding up and down Simon's length inside of his boxer shorts.

Grabbing her by the shoulders, Simon hastily looked around. "N—Nothing."

They were in the alley, Magnus's front door was closed, and everything seemed fairly calm. There was no angry Shadowhunter, no smirking warlock, and thankfully, no beatings he shouldn't be receiving. It had all been a product of his imagination, brought on by sheer hunger. And maybe a small bit of terror.

"Come inside. You look hungry," she said, pulling Simon's attention away from the empty alley.

Simon shook his head. "Uh, why don't we go to Jordan's place tonight instead?"

"What's gotten into you?" Isabelle laughed, tugging him through the door by the front of his pants. Simon made a face, but hesitantly followed, unable to stop the aching between his legs. He couldn't resist Isabelle or his thirst. "You can drink from me, it's alright. We'll be sneaky about it." She leaned back against the wall, exposing her neck. "No one will find out."

_No one will find out_.

_Famous last words_, thought Simon as the first drop of Isabelle's blood hit his tongue.


End file.
